This invention relates to electric meters and indicators, and particularly relates to DC level indicators in which the DC level is represented by an analog quantity--here by a color as it appears to a person looking at the indicator.
Various meters are known that indicate a signal level by the position of a hand or lever or by a digital display on the face of the meter.
Indicators are also in use in which lamps are lit or extinguished in accordance with the level of an input signal. Normally, in such indicators, the only apparent indication is the lamp intensity (i.e., OFF, partially ON, or ON), or, if several lamps are used, the number of lamps that are lit.
Such indicators do not give a very good indication of how far the detected level is from some threshold or desired level. For instance, if the lamp is a speed indicator, it will indicate underspeed (OFF) or overspeed (ON) but does not alert an observer to the degree of overspeed or underspeed.
A multiple-lamp indicator requires the observer to count the number of lit lamps, and as such requires the observer to concentrate, and does not permit him to determine the level by a casual glance or, if many levels are being monitored, to monitor all the levels quickly.
By contrast, if the measured level were represented by the color of light, an observer would be able to determine changes in the level at a glance. Also, if many conditions are being monitored at once, and if a color, rather than a conventional meter reading, were used for each of the conditions, the observer could quickly determine any conditions that might be changing sufficiently, for instance, to indicate a trend toward malfunction.